Bottom Job repair question - is this gelcoat?

Scott T-Bird · Tuesday at 9:33 AM

If you can, find out from the previous owner what they used for bottom paint. It looks to me that the dark paint is a "hard" ablative by the way it chips. It seems too glossy to look like a soft ablative. Where are you located? Salt or fresh water? That would certainly make a difference for the paint they chose.

The white underneath looks a little like an orange peel texture so it does not look like gel coat to me. My guess is that it is an epoxy barrier coat applied over the gel coat. If it is barrier paint, it should have been done in multiple layers, and probably it was. You should not have to sand thru the barrier coats. I would simply sand around the patches to feather the edges before applying new paint. That would be the simple and effective job.

If you really want a perfectly smooth hull, you might want to fair the patches to blend with the existing paint. But first step is to try to determine what the surface paint is. You will need to know the existing paint to avoid any incompatible resurfacing that you might do. Once you know, then follow the recommended procedures based on the product.

Scott T-Bird · Tuesday at 9:37 AM

Lake Champlain? If so, Pettit VC-17 seems to be a popular paint for freshwater performance. You may have multiple layers as seen by the thickness of the chipped areas.

higgs · Tuesday at 6:55 PM

While northern sailers in fresh water usually use VC17, it would probably not adhere to that bottom paint given it's glossy appearance. Once on, VC is very easy to maintain and apply and does a good job in fresh water, but to use it would probably necessitate a bottom strip. I have used the paint for years on several of my boats and loved it.

Project_Mayhem · Tuesday at 7:29 PM

I bought a boat that the last owner said he gained an entire knot by switching to VC17. I will warn you against stripping the bottom if you can. It take a LOT of work. We tried a bunch of different sandpaper on the random orbital sander. Mirka was the best. It cut faster and clogged less

Tally Ho · Wednesday at 6:12 AM

I don’t think the bottom paint looks like VC17. Way too thick

And I think it only comes in 3 colors (black, blue and red).

Greg

Project_Mayhem · Wednesday at 6:14 AM

Tally Ho said:
I don’t think the bottom paint looks like VC17. Way too thick

And I think it only comes in 3 colors (black, blue and red).

Greg

And copper bronze

Tally Ho · Wednesday at 6:15 AM

Project_Mayhem said:
And copper bronze

That is what I call red…

JBP-PA · Wednesday at 7:19 AM

Viasatmatt said:
Thanks so much for this, Scott. I think I can reach the previous owner re: what bottom paint was last used. The boat is now in Lake Champlain, but the boat came from Boston, where it would have been painted last.

So, to summarize, your thinking is that the chips are in the bottom paint, not the gelcoat, so that the simplest fix is to sand down the chip edges, and simply repaint. The more thorough solution might be to sand the edges, then fair the remaining indention before painting. If I were to fair the indentions to make them smooth, do you have a recommendation for what I would use to do that fairing?

@Scott T-Bird is spot on. It looks like years of paint that is flaking off in some places. You should not add any fairing.

Ideally you would strip all the existing paint, but that isn't going to buy you anything other than blood, sweat, and tears.

A good solution is to heavily sand all the existing paint to get rid of some of the layers instead of completely stripping it. Repaint with VC17 which had very low build up. Repeat sanding every paint job and it'll be fine.

The easiest way is to just feather out the edges of the old paint. If you feather out a long way you won't even see it and you will not notice any performance difference.

JRacer · Wednesday at 8:55 AM

Tally Ho said:
I don’t think the bottom paint looks like VC17. Way too thick

And I think it only comes in 3 colors (black, blue and red).

Greg

Agree

Scott T-Bird · Wednesday at 9:47 AM

Tally Ho said:
I don’t think the bottom paint looks like VC17. Way too thick

Yes, I only guessed VC17 because I thought freshwater, but given that the boat came from Boston it most certainly isn't VC17. I also thought the thickness didn't look right for it. I don't have any experience with VC17 so I wouldn't know what years of build-up could look like.

I'm assuming that an Alerion would be particularly well cared-for given its pedigree, but they were first introduced in 1990 so 20 plus years of bottom paint build up can look very rough by now (without unusual maintenance). The photo was too small to see the entire condition but there does appear to be significant thickness inconsistency as well as the chips, which look rather small. We don't know if there are much larger areas where paint is flaking. I am curious about how glossy the paint looks. Could it have been wet when the photo was taken? It looks unusual to me anyway.

I agree with recommendation to rough sand the entire bottom, clean and apply new VC17 but be careful to know what you are sanding and make sure your preparation is consistent with VC17 instructions for compatibility over existing paint. (I don't have the knowledge for that).

I've done both procedures. I had the bottom soda-blast down to gelcoat, faired with epoxy to smooth out the micro-blisters, applied 3 coats of barrier and 2 bottom coats of my Starwind 27 for over $4K back in 2016 for the pros to do it. It was very satisfying because the bottom really needed that work to be done.

My Catalina had a much better bottom condition but I was getting concerned last spring (2025) about the paint build-up and flakes I started to see after several years. I sanded with random-orbit and 60 grit in preparation. I tarped the gravel surface under the boat and our marina required the sander to have vacuum pickup. Over 2 days, I sanded for at least 8 hours total to get the bottom looking very smooth but I hadn't gone thru all the bottom paint. It was a difficult 2 days, I ain't gonna lie. But the paint looked exceptional when I was finished re-applying the ablative paint.

Sanding with random orbit was very tedious and agonizingly slow for almost the entire job. As it turned out, my random-orbit function stopped functioning (broke) near the very end of the job. Instead, the sander just spun like an orbital sander and I was astonished to see how rapidly sanding then went thru all the paint layers with very little pressure. Actually, I couldn't figure out why it just started sanding the layers right thru and I had to finish the job very delicately because I didn't want to go thru the barrier coat and expose gelcoat. I had some small, damaged areas that I had to repair before painting! Be careful if that ever happens to you!

Tally Ho · Wednesday at 2:51 PM

Almost no build up with VC17. It goes on almost like water (ok, not quite that thin, but very thin). You never have to sand off the old paint.

And it dries in about a minute if it is warm and breezy out. I often paint the stand ”squares” while the yard guys are lifting her in the sling...and the paint is dry before we hit the water.

Greg

Bottom Job repair question - is this gelcoat?

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